I have used this with success. You need to make sure that UBX protocol is enabled for both input and output on the port you are using with ser2net. The other thing to check is the "Acknowledge Aiding Input" on the NAVX5 configuration section. This needs to be enabled for the "smart" data load.
FYI, I have also added AssistNow Online support to my github repository "rasp-gps-ntp' so that the module gets configured on startup. It dropped the time-to-first-fix for me to about two minutes.